FIG. 1 illustrates a representative prior art digital telephony conferencing system. The conferencing system consists of numerous participants at locations 1 through n. One of more telephones 5 may be located at each location. A multiplexing and demultiplexing device 4 connects each of the telephones to the conference bus 3. Some locations may have only a single user, while other locations may have multiple users. Each user will be individually connected through a multiplexer 4. A time-division multiplexing (TDM) bus 3 conveys the signal information generated by each participant to all other participants of the system.
FIG. 2 illustrates a representative frame of the information communicated by the TDM bus 3 during one frame period, τ. In the exemplary embodiment, the frame period, τ, is 0.5 msec and four eight-bit digitized and encoded samples, illustrated as sample 1 through sample 4 are required to adequately represent the signal information communicated by one participant in this period of time. The four samples from each participant are sequentially grouped together within the TDM frame to form a TDM time slot. For a number of participant groups, group 1 through group n, the total number of payload bytes the TDM frame must support is given by the equation:Tbytes=(4 bytes/participant)*(n participants).For 30 participants the system requires 30 TDM time slots every 0.5 ms and a total of 120 bytes of information in a frame.
Although the specific parameters, such as frame period or sample size, of an exemplary conference can vary, the size of the data payload will be dependant upon these factors and upon the number of participants.
When a large number of people participate in a telephony conference, there is a significant likelihood that two or more participants will speak at the same time. It is also likely that background noise originating at one or more group nodes will be transmitted through the conferencing system. The transmitted signals of the background noise and multiple speakers interfere with the signal that is of interest to the conference participants. These interfering signals impair the ability of the conference listeners to hear and understand the speaker that is of interest to them and thereby reduce the quality of the communication.
Further, the transmission of background noise, as well as the transmission of other speakers in addition to the primary speaker places an additional load on a communications system.
To overcome these problems, some conferencing systems limit the number of signals that may be heard by the conference participants. This is accomplished by muting all but the loudest signals originating at the telephones of participants in the conference. Typically, a system may limit transmission to three separate signals of three speakers who are talking simultaneously from among a large number of participants. The remaining signals which were transmitted to the central processor will be muted and therefore not provided to the remaining participants.
In order to determine which of the participants are the loudest, a central processor 6 for the system must receive all of the input signals from each of the participants and perform a comparison. Transmission of all input to a central DSP requires significant bandwidth, especially if there are a number of participants. Further, processing of all signals for strength comparison can require significant processing resources. The use of a single control DSP 6 will require significant processing resources in a single DSP and can cause delay.